It is known in principle that during CT methods, scattered radiation effects are produced that lead to inaccuracies in the measurement of the absorption of X-radiation. Considering this effect, firstly, in the case of a single focus/detector system, the problem of scattered radiation becomes more severe here the wider the ray fan used is expanded, since the locations at which scattered radiation is produced increase correspondingly.
To counteract this known effect, there are fitted upstream of the detector in the case of such CT systems so-called scattered radiation collimators that uncover upstream of each detector element only the direct beam direction between detector element and focus, and largely shade all the other directions. Such scattered radiation collimators are also used in the case of two-focus or multifocus/detector systems. However, these scattered radiation collimators cannot reduce the scattered radiation that is produced by beams of another focus arranged in an angularly offset fashion, and that has the same spatial orientation as the actual direct beam that originates from a focus opposite the detector and whose intensity is to be measured.
There is thus the fundamental problem of determining the fraction of this scattered radiation in the overall measured intensity of the radiation, and of correcting the measured radiation intensity by this fraction so that the reconstruction uses actually only attenuation of the direct irradiation striking a detector element. Artifacts are otherwise produced in the CT display.
A known method for scattered radiation correction in a two-focus/detector system is disclosed, for example, in patent specification DE 102 32 429 B3. In the case of this patent specification, two focus/detector systems arranged angularly offset from one another are operated in an alternating fashion at least temporarily, such that the scattered radiation actually occurring and originating from the focus/detector system being operated can be measured directly in the focus/detector system respectively not switched on.
In order to carry out this method, it is necessary to operate the X-ray sources in an alternating fashion at least temporarily, as a result of which at these times image information from the CT scan is lacking at least in the detector of the X-ray tube that is not being operated, and so gaps are produced in the data acquisition. This is disadvantageous, particularly in the case of CT cardio pictures, which require a high time resolution, and this method leads in practice to deficient recording results.